Stratospheric Disturbances Research Articles

Enhanced stratosphere-troposphere and tropics-Arctic couplings in the 2023/24 winter

The stratosphere-troposphere and the tropics-Arctic couplings were intermittently enhanced in the 2023/24 winter. Here we used ERA5 reanalysis data and found that due to the amplification of planetary wavenumber 1 and 2 pulses, three displacement-type sudden stratospheric warming events occurred in one winter under the background conditions of warming equatorial middle and east Pacific, active equatorial convections, and easterly stratospheric equatorial winds. During the sudden stratospheric warming events, the stratospheric disturbances propagated downward to the surface, followed by continental cold surges. The residual meridional circulation was strengthened across the tropics and Arctic, anomalously more water vapor was transported into the stratosphere in tropics, while ozone content diminished in the lower stratosphere and grew in the upper stratosphere over the tropics. Meanwhile, water vapor and ozone over the Arctic exhibited a dipping pattern from the upper to the lower stratosphere.

Identification of stratospheric disturbance information in China based on the round-trip intelligent sounding system

Abstract. Assessing the role of physical processes in the stratosphere under climate change has been one of the hottest topics over the past few decades. However, due to the limitations of detection techniques, stratospheric disturbance information from in situ observations is still relatively scarce. The round-trip intelligent sounding system (RTISS) is a new detection technology, developed in recent years, that can capture atmospheric fine-structure information about the troposphere and stratosphere via three-stage (rising, flat-floating, and falling) detection. Based on the structure function and singular measure relationships, we quantify stratospheric small-scale gravity waves (SGWs) over China, using the Hurst and intermittency parameters, and discuss their relationship with inertia-gravity waves (IGWs). The results show that the enhancement of SGWs in the stratosphere is accompanied by weakening of the IGWs below, which is related to the Kelvin–Helmholtz instability (KHI), and is conducive to the transport of ozone to higher altitudes from lower stratosphere. The parameter space (H1, C1) shows sufficient potential in the analysis of stratospheric disturbances and their role in material transport and energy transfer.

Stratosphere-troposphere coupling during stratospheric extremes in the 2022/23 winter

Using the ERA5 reanalysis, sea surface temperature, sea ice observations, and the real-time multivariate Madden-Julian Oscillation (MJO) index, the evolution of the stratospheric extreme circulation in the winter of 2022/2023 is explored. The stratospheric polar vortex was disturbed three times in the 2022/23 winter, contrasted with only one disturbance during the other three recent winters with an SSW. Possible favorable conditions for the strong stratospheric disturbances and their effects on stratospheric ozone, water vapor distribution, and near-surface temperature were examined. Around 7 December 2022 when a short but strong pulse of planetary wavenumber 2 appeared from the troposphere to stratosphere, a weakened and elongated stratospheric polar vortex formed at 10 hPa. This pulse is related to the intensifying Ural ridge and the deepening East Asian trough. After the first stratospheric disturbance, a large fraction of cold anomalies occurred in the Eurasian continent. A lagged impact after these stratospheric disturbances was observed as strong cold anomalies formed in North America from 13 to 23 December. On 28 January 2023, a minor SSW event occurred due to a displacement of the stratospheric polar vortex. A strong pulse of eddy heat flux contributed alternately by planetary wavenumber 1 and 2 showed a large accumulative effect on the stratospheric disturbance. However, the downward impact of this second disturbance was weak, and cold surges were not noticeable after this minor SSW. The third stratospheric disturbance this winter is a major displace-type SSW that occurred on 16 February 2023, and the total eddy heat flux primarily contributed by planetary wavenumber 1 increased rapidly. Following the major SSW, the North American continent was covered by large patches of strong cold anomalies until the end of March. During the three disturbances, the residual circulation correspondingly strengthened. The water vapor and ozone in the middle and lower layers of the polar stratosphere showed positive anomaly disturbances, especially after the major SSW onset. The unprecedented frequent stratospheric disturbances in winter 2022/23 were accompanied by severe loss of Barents-Laptev Sea ice and anomalously cold tropical Pacific sea surface temperatures (La Niña), which have been reported to be conducive to the enhancement of planetary waves 1 and 2 respectively. Further, two weeks before the major SSW, existing MJO developed into phases 4–6, also contributing to the occurrence of major SSW.

Effects of Energetic Particle Precipitation on Stratospheric Temperature During Disturbed Stratospheric Polar Vortex Conditions

AbstractRecently, observational and re‐analysis studies have outlined potentially enhanced influence of Energetic Particle Precipitation (EPP) either at times preceding Sudden Stratospheric Warmings (SSW) or when the distribution of planetary wave activity is suitable. In addition, significant correlations have been found between EPP and the occurrence rate of SSWs when the phases of the Quasi‐Biennial Oscillation (QBO) are taken into account. Here we study the influence of EPP during disturbed stratospheric polar vortex conditions using chemistry‐climate model SOCOL‐MPIOM3 over the 20th century. When classifying disturbed conditions, the definition of minor SSWs are utilized along with a temperature gradient (day‐to‐day variations) criteria at 90°N and 10 hPa acting as a measure of the strength of the events. We find no influence of EPP on the occurrence rate of disturbed conditions over the last 100 year period. However, conditions preceding and during the disturbances are significantly different when EPP forcing is included into the model. This is especially true for stratospheric disturbances occurring in February. Furthermore, there is a clear tendency that the EPP effect becomes more notable after the 1950s. Our results imply that EPP forcing could be important for the stratospheric conditions during winter and that pre‐conditioning forced by atmospheric disturbances are an important factor when considering how the mechanism operates.

On the Upward Extension of the Polar Vortices Into the Mesosphere

AbstractThe polar vortices play a central role in vertically coupling the atmosphere from the ground to geospace by shaping the background wind field through which atmospheric waves propagate. This work extends the vertical range of previous polar vortex climatologies into the upper mesosphere. The mesospheric polar vortices are defined using the CO gradient method with Microwave Limb Sounder satellite data; the stratospheric polar vortices are defined using a stream function‐based algorithm with data from meteorological reanalyses. Strengths and weaknesses of the two vortex definitions are given, as well as recommendations for when, where, and why to use each definition. Midwinter mean vortex geometry in the mesosphere is funnel shaped in the Arctic, with a wide top and narrow bottom. The Antarctic mesospheric vortex tapers with height in early winter and broadens with height in late winter. The seasonal evolution of mesospheric vortex frequency of occurrence, size, and zonal symmetry in both hemispheres is presented. Unexpected behavior above 60 km includes late season vortex broadening in both hemispheres, especially following winters without sudden stratospheric warmings. Following extreme stratospheric disturbances the polar night jet in the mesosphere strengthens and shifts poleward, resulting in a mesospheric vortex that contracts. Overall, the mesospheric polar vortices are more similar between the two hemispheres than their stratospheric counterparts. The vortex climatology presented here serves as an observational benchmark to which the mesospheric polar vortices in high‐top climate models can be evaluated.

Changes in the total ozone distribution in the atmosphere over Antarctica

The data obtained by the authors during the last decade from satellite measurements in 1979–2016 and related to changes in zonal asymmetry of the Antarctic ozone and to their coupling with atmospheric parameters in the Southern Hemisphere are summarized in this work. The spring levels of the Antarctic ozone in 2000s–2010s do not show increase of the ozone hole size observed in 1980s–1990s. Stabilization and the first evidence of the ozone hole area decrease are considered as consequence of Montreal Protocol 1987 on restriction of emissions of ozone depleted substances into the atmosphere. Long3term changes of total ozone content in atmosphere over the Antarctic region in spring are accompanied by changes in its asymmetric distribution relatively the South Pole. Interannual variations of the longitudinal ozone minimum position demonstrate statistically significant relation to structure of the quasi3stationary planetary waves in distribution of atmospheric parameters. Long3term longitudinal shift of the ozone minimum is similar to shift in zonal structure of planetary waves in the tropospheric parameter distribution and is also accompanied by meridional displacement of the climatic anomalies toward the equator. The obtained relationships characterize interdependence between the large3scale tropospheric and stratospheric disturbances in the Southern Hemisphere during the ozone hole season.

Westward traveling planetary wave events in the lower thermosphere during solar minimum conditions simulated by SD-WACCM-X

We present numerical simulations with the Whole Atmosphere Community Climate Model, eXtended version (WACCM-X), whose dynamics is constrained by atmospheric specifications during recent and historical solar minimum conditions. The focus of this study is to describe how various dynamical conditions of boreal winter affect the dynamical behavior of the lower thermosphere (90–150km). The model simulations are carried out during solar minimum conditions and the results shown here discuss the period January 1–March 30 for five years (1995, 1996, 2008, 2009, and 2010). These years were selected because they include boreal winters without stratospheric warming (1995 and 1996), with modest or normal stratospheric warming (2008 and 2010), and with a large and persistent stratospheric warming (2009). The ultimate goal of this study is to encapsulate the statistically significant dynamical behavior due to westward propagating, planetary-scale waves (wavenumber 1 and wavenumber 2) in the lower thermosphere that are associated with different stratospheric conditions. To this end we show that the westward zonal acceleration above about 80km is by and large described by traveling waves with periods between 2 and 10 days. We show that the momentum carried by these waves is unlikely to affect directly the momentum budget of the extra-tropical lower thermosphere, where instead gravity-wave drag figures prominently. However, at the times leading to and following large stratospheric disturbances, we show prominent meridional propagation of wave activity from the mid-latitudes toward the tropics. In combination with strong eastward meridional wind shear, our results provide further evidence that such equatorward propagation of momentum in the lower thermosphere might influence the amplitude of equatorially trapped tides.

The 2009–2010 Arctic stratospheric winter – general evolution, mountain waves and predictability of an operational weather forecast model

Abstract. The relatively warm 2009–2010 Arctic winter was an exceptional one as the North Atlantic Oscillation index attained persistent extreme negative values. Here, selected aspects of the Arctic stratosphere during this winter inspired by the analysis of the international field experiment RECONCILE are presented. First of all, and as a kind of reference, the evolution of the polar vortex in its different phases is documented. Special emphasis is put on explaining the formation of the exceptionally cold vortex in mid winter after a sequence of stratospheric disturbances which were caused by upward propagating planetary waves. A major sudden stratospheric warming (SSW) occurring near the end of January 2010 concluded the anomalous cold vortex period. Wave ice polar stratospheric clouds were frequently observed by spaceborne remote-sensing instruments over the Arctic during the cold period in January 2010. Here, one such case observed over Greenland is analysed in more detail and an attempt is made to correlate flow information of an operational numerical weather prediction model to the magnitude of the mountain-wave induced temperature fluctuations. Finally, it is shown that the forecasts of the ECMWF ensemble prediction system for the onset of the major SSW were very skilful and the ensemble spread was very small. However, the ensemble spread increased dramatically after the major SSW, displaying the strong non-linearity and internal variability involved in the SSW event.

Polar vortex evolution during Northern Hemispheric winter 2004/05

Abstract. As a part of the project "Atmospheric Wave Influences upon the Winter Polar Vortices (0–100 km)" of the CAWSES program, data from meteor and Medium Frequency radars at 12 locations and MetO (UK Meteorological Office) global assimilated fields have been analyzed for the first campaign during the Northern Hemispheric winter of 2004/05. The stratospheric state has been described using the conventional zonal mean parameters as well as Q-diagnostic, which allows consideration of the longitudinal variability. The stratosphere was cold during winter of 2004/05, and the polar vortex was relatively strong during most of the winter with relatively weak disturbances occurring at the end of December and the end of January. For this winter the strongest deformation with the splitting of the polar vortex in the lower stratosphere was observed at the end of February. Here the results show strong latitudinal and longitudinal differences that are evident in the stratospheric and mesospheric data sets at different stations. Eastward winds are weaker and oscillations with planetary wave periods have smaller amplitudes at more poleward stations. Accordingly, the occurrence, time and magnitude of the observed reversal of the zonal mesospheric winds associated with stratospheric disturbances depend on the local stratospheric conditions. In general, compared to previous years, the winter of 2004/05 could be characterized by weak planetary wave activity at stratospheric and mesospheric heights.

Dynamical Climatology of the Upper Mesosphere, Lower Thermosphere and Ionosphere

The main features of upper atmosphere dynamics as an important part of upper atmosphere climatology are presented. The dynamics of the mesosphere and lower thermosphere (MLT) are of special interest. The results are based on the long series of investigations in East Siberia and data from a world-wide network of observatories. We present the regional climatic norms for the prevailing wind and semi-diurnal tide and the main features of the quasi-periodic structure of the wind field. The non-zonality of MLT dynamics is demonstrated as well as regional differences in the response of the wind field to stratospheric disturbances, solar activity variations and geomagnetic storms.

A model study of the dynamical connection between the Arctic Oscillation and stratospheric vacillations

The dynamical connection between the stratosphere and the troposphere in the Northern Hemisphere winter is investigated with general circulation model (GCM) simulations under perpetual January conditions. The variability in the stratosphere is strongly dominated by vacillations on a timescale of 100 days. One‐point correlation maps of the zonal mean zonal wind reveal the characteristic downward propagation of the stratospheric disturbances. The meridional structure of the stratospheric vacillations is well described by a few empirical orthogonal functions (EOFs) of geopotential height. The leading EOF describes a standing oscillation of the stratosphere, while the two next describe the vertical and horizontal propagation. In the troposphere the leading EOF of the surface pressure shows the characteristic circumpolar structure of the Arctic Oscillation. The covariance between the leading EOF of the surface pressure and the zonal mean zonal wind reveals a vertical structure similar to the observed below 10 hPa, while the sign of the covariance changes above 10 hPa where observations are scarce. The downward propagating stratospheric modes play a prominent role in the vertical coupling. Singular value decomposition of the cross‐covariance matrix between the stratospheric zonal mean zonal wind and the surface pressure shows that a significant part of the tropospheric variability can be related to the downward propagating anomalies. The leading pattern of surface pressure anomalies found in this way closely resembles the pattern of the Arctic Oscillation and describes 20–30% of the total variance. This result is confirmed by studying the covariance between the geopotential height fields and the stratospheric principal components.

Far infrared observations of travelling stratospheric disturbances

Travelling ionospheric disturbances (TID) have been reported by various authors in the past: they have been observed in the ionosphere by means of indirect techniques, like disturbances in the propagation of radio-waves. Mesospheric disturbances, like noctilucent clouds, (NLC) have been also widely quoted in literature, being observed through the Sunlight scattering in night time. We present observations of TSD (travelling stratospheric disturbances) during the stratospheric balloon program ULISSE devoted to the study of sky brightness in the wave-length region 300–3000 micron. The observed TSD appear to be localized at a typical altitude of 80–150 km with peculiar velocities of 50–200 m sec −1. Spectral properties of the emitted radiation have been investigated by means of multichannel photometers: two types of TSD have been found. The first one has a spectral emissivity consistent with the standard stratospheric composition (H 2O and O 3 being the most important emitters): the second type of TSD, observed about one month after St. Helen explosion in 1980, has the typical spectrum of dust with an emissivity ϵ ≅ 1/λ and an abundance of the order of 10 particles per cm −3 with submicron radius.

Gravity waves and turbulence associated with cumulus convection observed with the UHF/VHF clear‐air Doppler radars

Vertical wind disturbances are frequently observed during midsummer afternoons in association with cumulus convection. To examine the relation of these wind disturbances to atmospheric stability and turbulence intensity, we carried out intensive observations of wind, temperature and humidity over a large vertical region extending from the boundary layer to the lower stratosphere using UHF/VHF radars and radiosondes at Shiga, Japan (35°N, 136°E). The wind disturbances propagate quickly into the upper troposphere just after 1500 local standard time (LST) when the level of free convection (LFC) descends below the top of the mixed layer, while before that, the disturbances are confined in the mixed layer. However, strong turbulence is largely confined to the region below 3 km even after 1500 LST, suggesting that the height of 3 km corresponds to the top of cumuli, while the wind disturbances above are due to gravity waves generated in association with cumulus convection. In addition, stratospheric disturbances were examined for 12 cases of midsummer disturbances using routine observational data taken with a VHF radar in a height region of 5–24 km. Wind disturbances are observed in the lower stratosphere when turbulence as well as wind disturbances are strong in the whole troposphere. The stratospheric disturbances are dominant in two regions below and above a height of 18 km where the background horizontal wind is weak. Long‐period disturbances are observed only in the lower region. This fact suggests that the height of 18 km is a critical level for the long‐period gravity waves. The existence of a strong turbulent layer around 18 km is consistent with this inference.

Some features of the vertical ozone distribution from millimeter wave measurements at Pushchino and Onsala observatories

A number of features of the stratospheric ozone distribution were revealed by joint millimeterwave observations of ozone emission lines at 142,175 and 110,836 GHz carried out during the winter periods of 1988–1989 and 1989–1990 at the Radioastronomical Observatory of the P.N. Lebedev Physical Institute of the Russian Academy of Sciences and at the Onsala Space Observatory of Chalmers University of Technology, Sweden. It is shown that vertical ozone variations observed at the two observatories were connected with large scale dynamical processes that occurred in the stratosphere. When the stratosphere was relatively undisturbed the ozone profiles obtained at both observatories were close to the ozone reference model given by Keating and Pitts. There were periods during a stratospheric warming when the ozone content measured at the two observatories in the 25–40 km altitude range was higher by a factor ~ 1.5 than the model values. Dynamical processes in the stratosphere also gave rise to rapid (4 h duration) and large deviations from the model ozone profile. An ozone layer depletion was observed in the 27–55 km altitude range. The observed ozone variations illustrate the sensitivity of the ozone distribution to stratospheric disturbances including stratospheric warmings.

Planetary-Scale Disturbances in the Southern Stratosphere during Early Winter

The stratospheric circulation and planetary-scale dusturbances during early-winter (mid-April to mid-July) in the Southern Hemisphere are investigated using observational data collected for the 1979-1990 period, and a 3D primitive equation model of the stratosphere and mesosphere. It was found that there were six extended periods in the data set when wave 1 (which is usually quasi-stationary) traveled steadily eastward and had large amplitude. Results of simulations suggest that the development of the South Pacific warmings is connected with the amplification of wave 1 at 100 mb. The results also indicate that the development of stratospheric disturbances in the southern stratosphere during early winter depends more on the intensity of wave 1 at 100 mb than on the structure of the zonal-mean flow in the stratosphere.

One-to-Two Month Oscillations in the Stratosphere during Southern Winter

Abstract Stratospheric disturbances on the 35–60 day time scale are investigated with particular emphasis on the Southern Hemisphere. The data used are stratospheric brightness temperatures from 90 to 1.5 hPa covering seven 6-month southern winter periods (from April 1980 to March 1987). Global time-lag correlation plots are constructed from which tropical/extratropical connections, three-dimensional wave structure, and propagation characteristics are studied. Horizontal correlation patterns at 90 hPa reveal a strong connection between the Indonesian tropics and the winter extratropics. Vertical correlation patterns in the southern winter extratropics reveal westward tilt with height and vertical propagation of 35–60 day zonal wavenumber 1 perturbations, from tropospheric regions up to great heights, at least as high as the stratopause region. Disturbances are found to propagate from 90 hPa to 1.5 hPa in generally 6 to 9 days. In contrast, the vertical correlation plots in the tropics indicate little or n...

On the Interannual Variability of the Upper Mesosphere during the Northern Winter and Spring

Derived thicknesses, using data from the Stratospheric and Mesospheric Sounder (SAMS) onboard the Nimbus 7 satellite, and 30-mbr height analyses, based on radiosondes, have been combined to provide monthly mean height charts of the upper mesosphere,(0.01-mbar level approx. 78-80km) Four years of charts are available, 1979-1982. Based on this material, the large interannual variability during the northern winter and spring is discussed, with emphasis on the effects of stratospheric warmings during midwinter and spring on the mesospheric circulation. It is shown that the effect of the winter and of the stratospheric disturbances on the upper mesosphere is different from year to year, depending on the timing of the stratospheric events. Such results are needed for the discussions about the representativeness of Reference Atmospheres.

Three‐dimensional simulations of stratospheric N2O: Predictions for other trace constituents

The Geophysical Fluid Dynamics Laboratory (GFDL) three‐dimensional general circulation/tracer model has been used to investigate the stratospheric behavior of N2O under a range of photodestruction hypotheses. A comparison of observations with these simulations shows that the atmospheric N2O lifetime lies between 100 and 130 years. For the three experiments conducted, it was found that the model‐derived global one‐dimensional eddy diffusion coefficients Kz for one experiment are appropriate for the other two experiments as well. In addition, the meridional slopes of N2O mixing ratio isolines are virtually identical in the lower stratosphere for all three experiments. The generality of these two results was explored with a simple “two‐slab” model. In this model the equilibrium meridional slopes of trace gas isolines and Kz values are solved directly. The model predicts that long‐lived gases with weak photodestruction rates should have similar meridional slopes, but the effect of faster destruction is to flatten the meridional slopes. The simple model also predicts that Kz depends upon chemical processes through a direct dependence upon the meridional slope for a given gas as well as upon the intensity with which upward propagating tropospheric disturbances force the stratospheric zonal winds. The three N2O experiments have been compared against detailed observational analyses. These analyses show that the model meridional N2O slopes are too flat by about 30%. The simple two‐slab model indicates that this results from a somewhat weak forcing of the model stratospheric zonal winds. A comparison of the temporal variability of model N2O against the “Δ” statistics of Ehhalt et al. (1983) shows good agreement. Another simple theoretical model is proposed that shows why Δ statistics are so useful and predicts the circumstances under which different destruction chemistries should lead to different Δ statistics. These results have allowed a very general extrapolation of the three N2O numerical experiments to predicted structure for a wide class of long‐lived trace gases. Specifically, the supporting theoretical developments allow predictions for the effect of chemistry on the global (one‐dimensional) behavior, meridional‐height (two‐dimensional) structure, and local temporal variability. Finally, some examples of transient behavior are presented through model time series at points corresponding to available measurements. These time series, with the support of horizontal N2O charts, show complex behavior, including pronounced seasonal cycles, transport‐produced N2O “inversions,” and detailed meridional transport events associated with transient stratospheric disturbances.

THE DISTURBED CIRCULATION OF THE ARCTIC STRATOSPHERE

The annual cycle of disturbed circulation in the arctic stratosphere (i.e., areas north of the main jet-core of the Ferrel westerlies) is discussed in the light of climatological and synoptic evidence. In summer, the Ferrel westerlies and their wave-trains choke off with height to a zero-level near 50 mb. Because of the warmth of the arctic stratosphere, easterly anticyclonic flow is continuous at higher levels. In August, cooling begins, and by September a barotropic westerly vortex, continuous with the Ferrel vortex, is established. In October and November, this vortex becomes baroclinic and appears distinct from the Ferrel westerlies. Winter circulation has two aspects: (1) warm, barotropic, anticyclonic flow associated with a strengthening and extension of the Alaskan warm ridge, which extends to above 25 mb; and (2) cold-low development near the pole, with a marked tendency for the development of a cold trough over eastern Canada. Polar-night jet-streams and travelling baroclinic waves characterize the outer parts of the cold-lows. The thermal waves associated with these disturbances often have large amplitudes and normally affect the entire stratosphere. The apparent independence of stratospheric disturbances centered above 50 mb is examined, and the probable physical and dynamical processes involved are tentatively discussed.